Abstract 3726: Postmenopausal hormone therapy use and mammographic density in Norwegian women

While studies have shown that the use of post-menopausal hormone therapy increases mammographic density, certain aspects of this association remain unclear. We examined whether mammographic density differs according to the type of hormone therapy used, dose, duration of use, time since last use, as well as whether the effects are modified by age and body mass index (BMI). We used a cross-sectional design and recruited 2265 post-menopausal women, aged 50-69 who participated in the Norwegian Breast Cancer Screening Program in 2004. Mammographic density was assessed with the computer-assisted method (Madena), and we estimated mean percent mammographic density, controlling for possible confounding factors. Statistical analyzes were performed for all women combined and by age and BMI. Mammographic density was higher among current hormone therapy users (percent density: 20.8%; 95% CI: 19.6-21.9%), than among former (18.7%; 18.1-19.3%) or never HT users (16.7%; 15.8-17.6%). Ever users of combined estrogen-progestogen therapy (EPT) had higher percent density (20.0%; 19.1-20.9%) than estrogen-only (ET) users (18.3%, 17.7-18.9%) and never users (16.7%, 15.8-17.6%), and the highest density was seen in current EPT users (21.4%; 20.1-22.6%). Time since last use was significantly associated with density, with women who quit more than 3 years ago having density similar to never users. Mammographic density declined with increasing age and BMI. In analyses stratified by BMI, we found higher densities with EPT use in all categories, with somewhat smaller differences between ever and never EPT users in women with BMI of 26 and higher. When stratifying analyses by age, mammographic density was similar in EPT users and never users in women aged 55 and below. However, this was not true in leaner women (BMI of 23 or less). Among these young women (55 or less) with low BMI (23 or less), EPT users had higher percent density than never users. The percent density was 26.8% (23.7-29.8%) in never users, and 31.7% (28.0-35.4%) in ever users. No statistically significant difference in density was found in women older than 62 years old with a BMI of 26 and above, with percent density of 6.8% (5.3-8.3%), and 9.3% (6.9-11.6%) in never and ever users, respectively. Higher mammographic density was seen in ever users of estradiol and norethisterone acetate regimens (Activelle and Kliogest) compared to other EPT. Mammographic density was higher in women using high rather than low doses of estradiol and progestogen. In conclusion, the highest mammographic density was found in EPT users compared to ET and never users, particularly in users of the norethisterone acetate regimens. This increase was bigger in women taking high rather than low EPT doses. The association between EPT use and mammographic density was modified by age and BMI. These results have important implications and should be considered when, for example, deciding on which type and dose of hormones to prescribe. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3726. doi:10.1158/1538-7445.AM2011-3726